1. Field of the Invention
The present invention relates to a structure of a centrifugal air blower used for a ventilating blower such as a duct fan and for an air conditioner, for example.
2. Background Art
An existing centrifugal air blower is provided with a tapered wall at the part opposite to the tongue near the discharge outlet of the scroll to make the air velocity near the discharge outlet uniform for suppressing pressure loss and noise generated due to airflow turbulence near the discharge outlet of the casing. Such an existing centrifugal air blower is disclosed in Japanese Patent No. 5303877 for example.
Next, a description is made of the existing example referring to FIG. 5.
As shown in FIG. 5, centrifugal air blower 101 is composed of casing 102 and impeller 103 contained in casing 102. Casing 102 is composed of inlet side panel 105 having inlet 104, spiral scroll 106, and motor-fixing side panel 108 fixing motor 107. Casing 102 is spiral so that the flow path cross-sectional area (i.e., the radially cross-sectional area in the area enclosed by the outer circumference of impeller 103, the inside of scroll 106, and the side panels) is gradually larger from tongue 109 toward rotation direction 110 of impeller 103.
Impeller 103 is fixed to motor 107. When motor 107 is driven to rotate impeller 103, inlet airflow 111 flows from inlet 104 into casing 102 through impeller 103. The air that has blown out from impeller 103 is pressure-boosted and converted from dynamic pressure to static pressure in casing 102, and flows out from discharge outlet 112 as discharge airflow 113. Tapered wall 114 is formed at the part of discharge outlet 112 opposite to tongue 109. Owing to tapered wall 114, the cross-sectional area formed by casing 102 cut along a plane vertical to rotation shaft 115 of motor 107 gradually becomes smaller toward the side panels (i.e., inlet side panel 105 and motor-fixing side panel 108).
In typical centrifugal air blower 101, the airflow velocity inside casing 102 is supposedly slower near the side panels (i.e., inlet side panel 105 and motor-fixing side panel 108). The difference in airflow velocity unstabilizes the airflow direction near discharge outlet 112 to generate a turbulent flow. With this structure, the cross-sectional area of casing 102 at the side panels (i.e., inlet side panel 105 and motor-fixing side panel 108), where the airflow velocity is slower, is made smaller by means of tapered wall 114, thereby increasing the volume of air passing through the unit area. That is, the slower velocity of airflow can be increased. In this way, increasing the airflow velocity near the side panels (i.e., inlet side panel 105 and motor-fixing side panel 108) makes the air velocity near discharge outlet 112 uniform to some extent, thereby decreasing airflow turbulence to some degree.